1. Field of the Invention
The present invention is directed to an X-ray exposure system of the type having an x-ray radiator containing an X-ray tube and provided with collimators for limiting the radiated X-ray beam, in which the x-ray radiator can be displaced translationally and/or rotated angularly for orientating the radiation beam in space, as well as a planar digital image receiver having a number of pixels, with no mechanical connection between the image receiver and the x-ray radiator.
2. Description of the Prior Art
In X-ray examinations of patients, it is important for the radiation beam that is radiated by the radiation source to strike the X-ray film after passing through that part of the patient that is to be radiographed, so that an image of the exposed location is produced. A mobile X-ray apparatus, e.g. of the type described in the brochure MOBILETT Plus of the company Siemens-Elema AB, is used with a film cartridge (cassette) having no mechanical connection with the X-ray source. The film cartridge is placed under the patient, often under the mattress on which the patient is positioned. The operator then orients the radiation field as desired relative to the film cartridge. The field of radiation is often made extra large in order to avoid the risk that it will fail to cause the film. This causes unnecessarily high doses of radiation, as well as worsened image quality due to scattered radiation. Moreover, this leads to repeat exposures, due to incorrect settings of the radiation field in relation to the cartridge.
An attempt to remedy this problem is described in U.S. Pat. No. 4,092,544. In this reference, an X-ray exposure apparatus having a light source is disclosed that is connected in fixed relation to the X-ray tube and the diaphragm thereof. Furthermore, markings are arranged on a part connected fixedly to the film cartridge. The light source and the aforementioned part of the film cartridge provided with markings are arranged so that the light from the light source is not interrupted by a patient radiographed with the X-ray apparatus. By observation of the location at which the light beam from the light source strikes the part fixedly connected with the film cartridge, as well as observation of how the light beam strikes the markings, it can be determined whether the edges of the film cartridge are parallel to the outer boundaries of the X-ray beam that strikes the film cartridge, whether the central ray of the X-ray beam strikes the center of the film cartridge, and whether a desired target film distance has been set.
In U.S. Pat. No. 4,167,675, an X-ray collimator is described in which a light source is used to produce a beam of radiation whose shape and position coincides with the shape and position of the X-ray beam. By this means, a visual display of the extension and position of the X-ray beam of radiation is produced. This visual display, however, cannot be used to adjust the X-ray beam to a film cartridge in those situations wherein the region of the patient that is to be exposed is located, possibly with a mattress, between the X-ray source and the film cartridge.